This invention relates generally to pistons, and more particularly to the casting of pistons.
It is known to make a composite piston from a combination of different materials to tailor the physical properties of the materials to the needs of different regions of the piston.
For example, U.S. Pat. No. 1,940,629 shows an upper head portion piston made of a light metal united with a prefabricated lower portion of copper-beryllium alloy by shrink fit or cast-in-place techniques. U.S. Pat. No. 4,334,507 shows an aluminum piston body having molded in place therein a prefabricated insert of a different material. U.S. Pat. No. 4,651,631 shows a piston body having two prefabricated parts joined by welding. U.S. Pat. No. 6,032,570 shows a piston body having dissimilar materials bonded together by a forging process.
Each of the above composite piston structures involves at least one prefabricated component which is joined by insert molding or to another prefabricated component by a secondary joining operation. The secondary operations add costs and complexity to the manufacture of composite pistons.
A composite piston constructed according to the present invention overcomes or greatly minimizes the limitations of the known prior art.
A dual alloy metallic piston constructed according to the invention includes a first portion and a second portion formed from a first alloy and a second alloy, respectively, with each alloy having a different composition. The alloys are separately and sequentially poured into a mold cavity such that the first alloy forms the first portion, preferably the head of the piston, while the second alloy forms the second portion, preferably the body of the piston. The first and second portions are joined at a transition zone which comprises a mix of the first and second alloys.
One advantage offered by the invention is that a piston assembly having dissimilar alloy components can be constructed by a simple process using a single mold cavity, thereby eliminating the usual secondary operations such as welding or bolting to join dissimilar alloy components together.
Other advantages of the invention include the elimination of additional materials and components to join the dissimilar alloy components together, reduced labor and time, elimination of specialized joining equipment, and a high strength, high integrity transition region between the regions.